1. Field of the Invention
This invention relates to a copper-based alloy which permits elimination or reduction of defilement with lead and excels in tolerance for dezincification, hot forgeability, or machinability, a method for the production of this alloy, and products using this alloy.
2. Description of the Prior Art
Generally in the copper-based alloys of this class, Cu-Zn brass alloys and Cu-Sn bronze alloys each having Cu as a main component are being used extensively.
Particularly, the brass alloys have been finding extensive dissemination because they are excellent in corrosion resistance, workability, forgeability, and mechanical properties and are also favorable in terms of price as compared with other copper-based alloys.
The brass alloys are known in various types such as, for example, free cutting brass (JIS [Japanese Industrial Standard] C3250, C3604), casting grade brass (JIS C3771), and brass (BS [British Standard] CZ132.
Particularly, the free cutting brass bar has a high Pb content of 1.8-3.7%. When it is used in a metallic part such as the valve which by nature operates in water, it encounters difficulty in satisfying the condition of the standard tolerance for Pb liquation (not more than 0.05 mg/liter, for example) because it liquates the Pb out into the water. The problem posed by such lead liquation, therefore, needs a prompt solution.
The free cutting brass bar is a brass material which has the xcex1+xcex2 phase for the texture thereof and, in relative ratios, contains Cu predominantly in the xcex1 phase and Zn likewise in the xcex2 phase. When this brass bar is retained in the atmosphere of a corrosive liquid, therefore, it forms a local cell from the potential difference between the xcex1 phase and the xcex2 phase and induces liquation of Zn and corrosion by dezincification.
Then, the ordinary forging grade brass bar combines the problem of liquation of Pb and the problem of corrosion by dezincification similarly to the free cutting brass bar.
As a measure against the problem of environment pollution due to this liquation of lead, the technique of producing blue brass incorporating Bi singly or Se and Bi jointly into a copper-based alloy in place of Pb with a view to eliminating the influence of the lead has been already suggested (U.S. Pat. No. 5,614,038)
Further, the technique of perfecting bronze by adding P to the technique for combating the lead as described above thereby forming an intermetallic compound, Cu3P, and enhancing the wear resistance thereof has been known (JP-A-08-120369). Various other techniques for combating lead have been suggested.
The conventional copper-based alloy materials have originated in the lead-combating technique which is directed at copper-based alloys. No technique which additionally excels in tolerance for dezincifiction as well as in machinability and forgeability has yet been known. No copper-based alloy which has solved a further particular problem of the tolerance for corrosion by dezincification peculiar to brass has yet been developed. Such is the true state of the conventional copper-based alloys.
This invention has been perfected as a result of a diligent study pursued with a view to solving the problems of the prior art. It is directed at clearing the problem of environmental pollution by the liquation of lead and, at the same time, providing a copper-based alloy of brass or bronze excelling in tolerance for dezincification, machinability, and hot forgeability.
To accomplish the object mentioned above, this invention contemplates, among copper-based alloys containing a component having a lower melting point than the base phase formed of the a phase, the xcex1+xcex2 phase, or the xcex1+xcex2+xcex3 phase, a copper-based alloy which has the machinability thereof enhanced by incorporating thereinto a component for dispersing the base phase and low melting component to disperse the low melting component uniformly therein.
In this case, it is made possible to decrease the resistance to cutting, improve the state of surface finish, or exalt the machinability including the evaluation of chips by adding Fe, B, etc. to finely divide the base phase, dispersing Bi as a low melting component, or uniformly dispersing Bi as a low melting component due to the addition of at least one member selected from the group consisting of Fe, B, and Se.
This Bi has the base phase thereof finely divided, exhibits a low melting point (271xc2x0 C.) similarly to Pb, possesses a lubricating effect because it melts by the heat evolved during the course of cutting, and consequently acquires enhanced machinability.
Further, the separated Bi is uniformly dispersed because the base phase can be finely divided by Fe or B or because intermetallic compounds (Zn+Se, Cu+Se) can be formed by Se.
Since the Bi is consequently fated to be distributed in the form of fine dots among the metal crystals, the alloy is enabled to uniformize the resistance thereof to cutting and succumb smoothly to cutting with the effect of lubrication as a contributory factor.
When the crystals are finely divided as described above, the Bi is uniformly dispersed on the crystalline interfaces and consequently enabled to impart an improved cutting property to the alloy.
The Bi or Pb is generally deposited in the grains and on the grain boundaries of the crystals. When Bi and Pb are added in equal amounts, one of them which is uniformly dispersed without segregation brings a greater effect of Bi and Pb on the cutting property of the alloy than the other. To be uniformly dispersed, the crystals must be finely divided. Besides the method which resorts to lowering the extruding temperature of a billet, this fine division of the crystals is accomplished, for example, by the addition of B and Fe, i.e. the means which is contemplated by this invention.
Since the resistance to cutting is decreased and the chips are finely shredded, the pertinent processing unit does not suffer the cutting blade thereof to be damaged within a prescribed length of time and enjoys improvement in machinability.